exec(1) 							   User Commands							   exec(1)

NAME

       exec, eval, source - shell built-in functions to execute other commands

SYNOPSIS

   sh
       exec [argument]...

       eval [argument]...

   csh
       exec command

       eval argument...

       source [-h] name

   ksh
       *exec [argument]...

       *eval [argument]...

   ksh93
       +exec [-c] [-a name] [command [argument ... ]]

       +eval [argument]...

DESCRIPTION

   sh
       The  exec  command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments and
       appear and, if no other arguments are specified, cause the shell input/output to be modified.

       The arguments to the eval built-in are read as input to the shell and the resulting command(s) executed.

   csh
       exec executes command in place of the current shell, which terminates.

       eval reads its arguments as input to the shell and executes the resulting command(s). This is usually used to execute commands generated as
       the result of command or variable substitution.

       source  reads  commands	from name. source commands can be nested, but if they are nested too deeply the shell can run out of file descrip-
       tors. An error in a sourced file at any level terminates all nested source commands.

       -h    Place commands from the file name on the history list without executing them.

   ksh
       With the exec built-in, if arg is specified, the command specified by the arguments is executed in place of this shell without  creating  a
       new  process. Input/output arguments can appear and affect the current process. If no arguments are specified the effect of this command is
       to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor  numbers  greater  than  2
       that are opened with this mechanism are closed when invoking another program.

       The arguments to eval are read as input to the shell and the resulting command(s) executed.

       On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

	   1.	  Variable assignment lists preceding the command remain in effect when the command completes.

	   2.	  I/O redirections are processed after variable assignments.

	   3.	  Errors cause a script that contains them to abort.

	   4.	  Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a
		  variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file  name  genera-
		  tion are not performed.

   ksh93
       exec is a special built-in command that can be used to manipulate file descriptors or to replace the current shell with a new command.

       If  command is specified, then the current shell process is replaced by command rather than running command and waiting for it to complete.
       There is no need to use exec to enhance performance since the shell implicitly uses the exec mechanism internally whenever possible.

       If no operands are specified, exec can be used to open or close files, or to manipulate file descriptors from 0 to 9 in the  current  shell
       environment using the standard redirection mechanism available with all commands. The close-on-exec flags is set on file descriptor numbers
       greater than 2 that are opened this way so that they are closed when another program is invoked.

       Because exec is a special command, any failure causes the script that invokes it to exit. This can be prevented by invoking exec  from  the
       command	utility.

       exec cannot be invoked from a restricted shell to create files or to open a file for writing or appending.

       eval  is  a shell special built-in command that constructs a command by concatenating the arguments together, separating each with a space.
       The resulting string is taken as input to the shell and evaluated in the current environment. command words are	expanded  twice,  once	to
       construct argument, and again when the shell executes the constructed command. It is not an error if argument is not specified.

       On  this  manual  page, ksh93 commands that are preceded by one or two + symbols are special built-in commands and are treated specially in
       the following ways:

	   1.	  Variable assignment lists preceding the command remain in effect when the command completes.

	   2.	  I/O redirections are processed after variable assignments.

	   3.	  Errors cause a script that contains them to abort.

	   4.	  They are not valid function names.

	   5.	  Words following a command preceded by ++ that are in the format of a variable assignment are expanded with the same rules  as  a
		  variable  assignment. This means that tilde substitution is performed after the = sign and field splitting and file name genera-
		  tion are not performed.

OPTIONS

   ksh93
       The following options are supported by ksh93 exec:

       -a name	  argv[0] is set to name for command.

       -c	  Clear all environment variables before executions except variable assignments that are part of the current exec command.

EXIT STATUS

   ksh
       The following exit values are returned by exec:

       0	Successful completion.

       1-125	A redirection error occurred.

       127	command was not found.

       126	command was found, but it is not an executable utility.

   ksh93
       The following exit values are returned by exec. If command is specified, exec does not return.

       0     Successful completion. All I/O redirections were successful.

       >0    An error occurred.

       The following exit values are returned by eval:

       If argument is not specified, the exit status is 0. Otherwise, it is the exit status of the command defined by the argument operands.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), ksh(1), ksh93(1), sh(1), attributes(5)

SunOS 5.11							    8 Apr 2008								   exec(1)